Glossary

Martin Parkinson’s T206 Glossary
T206 glossary
α- particle/radiation (alpha particle) – helium nucleus (i.e. 2 protons+2 neutrons). When emitted from a
nucleus during radioactive decay the resulting atom has moved two places lower in the periodic table.
Alpha radiation is the least penetrating type of radiation.
- decay/radiation (beta decay, beat minus decay)- form of radioactive decay in which a neutron turns
into a proton with the emission of an electron (aka  particle). A nucleus undergoing this type of decay
-
‘moves up’ one place in the periodic table because its atomic number increases by one. Beta radiation
can cause burns.
γ-particle/radiation (gamma particle) very short wavelength electromagnetic waves. Gamma emission
is a ‘settling down’ process, often following α or  emission or fission. Highly penetrating and the main
-
hazard associated with nuclear technology.
Aerosol – ESS p531 – tiny droplets of liquid as little as one micron in diameter. Cf vapour , particulate
Alternative vehicle fuels – (MTE ch2). ‘Overall, the use of alternative fuels presents a very mixed, and
extremely uncertain picture.’ (p21). Vehicle fuels other than petrol are:
 Diesel – CO2 emissions about 25% lower than petrol
 Compressed natural gas (CNG) – mainly methane – CO2 about 15 % lower (but cleaner in other
ways and well established
 Liquid petroleum gas (LPG) – mixture of propane (90%) and butane – reductions about the same
as diesel
 Ethanol/bio-ethanol – can be little or no improvement on fossil fuels depending on production
methods but ethanol from wood can be as high as 66%
 Methanol/bio-methanol
 Bio-diesel – same considerations as bio-ethanol
 Hydrogen – if produced from fossil oil, similar to LPG
CNG and LPG enable a more complete combustion than petrol or diesel and therefore reduction in
emissions
Anaerobic digestion – RE p127 – breakdown of biomass in the absence of oxygen. This happens in a
relatively uncontrolled way in a landfill, where the product of the organic component of the municipal
solid waste is known as landfill gas and in a controlled way in a specially constructed digester which
takes wet wastes (a feedstock of dung or sewage) and produces biogas.
Analysis:
Proximate analysis – defined ESS p174 analysis in terms of the combustion constituents
(moisture, volatile matter, Fixed carbon , ash)
Ultimate analysis – defined ESS p171 full chemical analysis of a sample (eg in the case of coal
carbon, hydrogen, oxygen, nitrogen, sulphur)
Annuitized costs – (ESS ch 12) capital costs spread out over a number of years, depending on lifespan
of project and chosen future discount rate. Can be calculated using spreadsheet PMT function.
Atmospheric pollutants – ESS p 532, and 521, - the full list of pollutants produced by energy generation
(excluding CO2)is:
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Martin Parkinson’s T206 Glossary
Cadmium
Carbon Monoxide
Dioxins
Furans
Lead
Mercury
Methane
NOx
Particulates
SO2
VOCs
Autoproducer - (ESS) organisation which generates electricity for its own use rather than relying on the
grid
Base load plants – (RE p399) large power stations, slow to start up and which therefore need to be kept
running, are said to deal with deal with the ‘base load’ – the demand that ‘will always be there’ despite
fluctuations.
The contrast is with peaking plant such as small open-cycle gas turbines (these lack the steam stage of a
CCGT) or diesel generators. These can be brought on line in minutes. The trade off is that they are less
efficient.
Even faster are the pumped storage hydros, which can be generating within 10 seconds.
Battery electric vehicle (BEV) – (MTE) with average European generating mix, about 40% cut in
greenhouse gases compared with petrol engine and 22% with diesel.
Beach Price - ESS 478 - used of crude oil to mean ‘price oil cost to get in to our country’. Beach price =
world price + cost of international transport.
Bergius process – a direct liquefaction method of coal liquefaction. Involves high temperature catalytic
conversion with H2
Betz limit – (RE p262) theoretical maximum fraction of the power in the wind which can be extracted –
16/27 or 59.3%.
Biomass/biofuels – the term which contrast with fossil fuels – in a renewable energy context, biologically
derived matter which was recently alive. RE p124 – ‘a feature of biofuels is that three quarters or more of
their energy is in the volatile matter (unlike coal where the fraction is usually less than half’). See also
energy crops. A list of biomass sources, apart from traditional biomass:
 Fast growing trees eg willow, hazel. Miscanthus – a C4 grassy plant
 Crop wastes e.g from sugar cane and rice (bagasse and rice husks)
 Residues from wheat and maize. Straw.
 Forestry residues
 Animal wastes: manure, sewage sludge, poultry litter
 Municipal solid waste
 Landfill gas
 Commercial and industrial wastes (eg furniture industry)
Biomass integrated gasification combined cycle (BIGCC) – (RE p115) this type of plant uses the
same principle as the CCGT, with the difference that its fuel is wood (therefore the gas from the wood
needs to be cleaned up before entering the turbines). The ARBRE plant in Yorkshire was to have been of
this type.
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Martin Parkinson’s T206 Glossary
Bio-oil – oil substitute produced from biomass by pyrolysis. (Re p133) It ‘usually has about half the
energy content of crude oil and contains acid contaminants.’
Boiler
C3 plants, C4 plants – RE p112 – categories of plants which reflect their slightly different photosynthetic
biochemistry. C3s are found in temperate regions, C4s in the tropics and C4s have a potentially greater
biomass yield because they avoid photorespiration.
Capacity factor – (ESS p 353, RE p152) Ratio of electricity produced over a given period to the
maximum it could produce running continuously & flat out. Usually expressed as a percentage. cf load
factor although ‘the two terms are often used interchangeably in the context of power plants’. Some
capacity factors:
Onshore wind – annual mean wind speed half the rated wind speed (‘moderate’) – 25% typical
Better sites can be 40% or more
Offshore wind – higher than this
Nuclear plant – high – 70% at least
Carbon capture and sequestration (CCS) – ESS p577. Methods of sequestration are:
 Forests – to keep the carbon pocked up in trees requires that once a forest is established it is
maintained. Reduction of the forested areas returns carbon to the atmosphere. The amount of
st
carbon likely to be emitted from burning of fossil fuels during the first half of the 21 century could
be sequestered in a forest areas equal to the area of Europe
 Biofuels – the same idea, but takes advantage of the plant growth by cropping it for fuels
 Beneath earth’s surface in:
o depleted oil/gas wells
o deep coal seams
o saline aquifers
In the case sequestration under the earth it is also necessary to have an active method of capture from
the flue gases of generating stations. The methods are:
 Absorption into a solid or liquid. Can be either:
o Chemical – where a chemical reaction takes place. Ethanolamines are sprayed into flue
2
gases. Can sequester 82%-99% of CO
o Physical – where CO2 is absorbed into organic solvents, which are themselves not
changed. This method moresuitable for IGCC.
 Adsorption – where the gas is taken up as a layer on the surface of a solid. 95% of CO2 can be
held. Again, this can be either:
o Chemical – gas held to the surface by chemical bonding
o Physical – held by van der Waals (weak electrical) forces.
 Gas separation membranes – allow one component of a gas stream to pass through faster than
the others. Relatively complex and costly in terms of price and energy.
Carbon dioxide emissions, relative – ESS p447 quotes the following estimates per GWh:
Nuclear, total fuel cycle emissions - 8.6 tonnes
Coal plant – 1058 tonnes
CCGT - 824
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Martin Parkinson’s T206 Glossary
Carbon Intensity – (MTE) “the amount of carbon released in combustion per unit of energy generated”
Catalytic converter – (ESS) Device which can be fitted to a conventional car to convert the exhaust
gases to less harmful substances. The gases are passed over 3 catalysts, (one each for hydrocarbons,
CO2 and NOx). The NOx is catalysed by rhodium and the reaction converts it back to nitrogen and oxygen.
Chain reaction – (ESS ch 11) after the fission of a nucleus, free neutrons are released. A neutron
absorbed into a nucleus can in turn cause it to fission, releasing more neutrons and so on.
To maintain a chain reaction (as in a nuclear power plant) requires a moderator because it is only slow
or thermal neutrons which cause fission.
Char – RE p124 – a term for the fixed carbon (see combustion, coal) left during the combustion of
biomass after the volatile matter has been released
CHP – (ESS p369) Combined Heat and Power aka ‘co-generation’. Conventional electricity generation
produces large amounts of low temperature waste heat: CHJP makes use of this for space and water
heating (one third of UKs delivered energy used for this).
Types of CHP:
 Large scale for autoproducers – eg large factories, chemical pants, oil refineries. Uses gas or
steam turbine plants. Accounts for most of the UK’s 5 GW of CHP
 Small-scale – usually a ‘small reciprocating engine similar to a car or trcuk engine but running on
natural gas’ Between 100 kW and 1 MW. Hospitals, community centres, large hotels.
 Large scale with community heating – relativelyt little in UK (example in Pimlico) uses exisiting
generating plant.
 Domestic scale – as yet not successfully developed despite interest.
CHP, potential – (ESS p371)
UK government aims to double CHP to 10 GW by 2010. Economic potential (for ditrcit heating, 6%
discount) might be up to 18 GW – 5 million homes.
Coal
Where? ESS p 166 and 13 reserves in North America (25%) Asia (23%) Former SS (22%)
Europe (11%) Australasian (9) Africa (8) South & central America (2)
How much is that? total 745 000 Mtce (p166)
Biggest users are: UK Figures for 2000:
Power stations – 73%
Coke 19%
Direct use 7%
Solid fuel 1%
What is it used for?
electricity 49%
iron & steel 32%
household 11%
other industry 8%
Coal gasification – (ESS p270) See IGCC
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‘Coal by wire’ – this phrase refers to the one-time dominance of coal in electricity generation – large coal
fired power stations were usually built near coal-producing areas.
Coal liquefaction – turning coal into synthetic oil. Two methods are: Bergius process (direct
liquefaction) and Fisher-Tropsch synthesis (indirect liquefaction).
Coefficient of performance (COP) - Ess p364 – of a refrigeration unit or heat pump is defined as the
ratio of Q2/W where Q2 is heat extracted from the evaporator. Carnot’s law applies here so:
T2
COPmax = -------------
(T1 – T2)
where T1 is the warmer temperature and T2 the colder. In practice values are quite low ‘typically about
2.5’.
Co-generation - an alternative term for CHP
Coke – ESS p161, 163. Fuel produced from the partial combustion of coal. Only certain types of coal
(coking coal) can be used to produce coke p171
Combined cycle gas turbine (CCGT) – (ESS). A CCGT plant uses a two stage process. natural gas is
burned and the resulting high pressure combustion gases drive a gas turbine. Because the combustion
o
temperature of natural gas is 1140 C the gases which exit the gas turbine are still hot enough to raise
steam which can drive another turbine.
In practice the maximum overall efficiency of the best coal-fired stations is just under 40% (an average for
coal fired stations is often quoted as 33%) whereas the overall efficiency of a CCGT can be over 50%.
Combustion
methane (ESS p 145)
CH4 + 2O2 - CO2 + 2H2O
pure carbon (ESS p 175)
C + O2  CO2
coal (ESS p173) process leading to complete combustion:
moisture
volatile matter (VM)
fixed carbon (FC)
Ash
Compression ratio – (ESS, MTE) ratio of cylinder size to compressed cylinder size which occurs during
the compression stroke of the four-stroke cycle
Condenser
Concentration ratio – (Re study guide p 14 Saq 22) – ratio of output to input in a solar concentrator. For
example: parabolic trough collector receives intensity of 500 W m-2 (input). Rate of heat loss from the
central tube is 1.5 W cm-2 (output) i.e. 1500 W m-2. Concentration ratio is 1500  500 = 30
Conventional oil – (ESS p278) contrasting term with non-conventional oil. Conventional sources are
crude oil sources which are ‘produced by natural pressure and contained within the subterranean
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Martin Parkinson’s T206 Glossary
reservoir’. Primary recovery refers to their recovery. Enhanced recovery techniques for conventional oil
are referred to as secondary recovery.
Conversions:
kWh to J – ESS p60-61 1kWh = 3,600,000 J
Coolant – (ESS ch 10) the heat exchange medium in a nuclear reactor. See also moderator.
Control rods – (ESS ch 10) A device for controlling the rate of fission in a nuclear reactor. Control rods
consist of a neutron absorbing material.
Cracking – (ESS p248) see oil refining
Cross compound – see turbine
Cross flow turbine – see turbines, types of
‘Dash for Gas’ (ESS p383) – the steep increase in gas-fired electricity plant which occurred in the UK in
the 1990s. The lead up to this was as follows:
1970s - discovery and exploitation of North sea oil and gas. Gas originally used domestically –
changeover from ‘town gas’
End of the ‘70s - 70% of electricity produced from coal – most of the rest from nuclear and oil
1984 – disputes with miners, start of running down of coal production
1989 – privatisation. CCGT technology well developed, plants cheaper, quicker to build, more
scalable, than coal or nuclear, new contractual arrangements (fixed price, 15 year)
1990-2000 – gas fired generation increased from 1%-39%
Degree-days – (RE study guide p30) - unit of difference between inside and outside temperatures. If on a
given day the average internal temperature was 18°C and the average external temperature was 8°C,
then the average difference would be 10°C. We would describe that particular day as having '10 degree-
days'. If the average external temperature was higher than the interior, the number of degree days would
be zero. The total heating requirement over a month will be proportional to the sum of all the degree-days
of the individual days. The more degree-days there are in a given month, the more heating a building is
likely to need.
Tables of degree-days are normally produced in the UK with standard internal temperatures such as 65°
Fahrenheit, equivalent to 18.3° Centigrade.
Delivered energy – see under energy
DERV – Diesel for Road Vehicles
Diesel – the diesel engine cycle differs from the four stroke petrol cycle in that it does not require a
spark for ignition. NOx emissions are higher than petrol engines (because of higher temperature), more
particulates (unburned hydrocarbons) because air/fuel mixture is critical and can be too rich. Also noisier.
Dioxins – ESS p21, 532 – chlorinated compounds, highly toxic, produced in small quantities in most
combustion processes and as by-products in some industrial processes. Produced if chlorine is present
Discounted cash flow analysis (DCF) – a DCF expresses a series of bills at various times in the future
as a single lump sum in the present.
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Discounting future payments - The process of expressing sums of money in the future in terms of
smaller sums today is
Distillation – see oil refining
Doping – (RE p67) – introduction of an impurity into a semiconductor.
Double Glazing – (RE p28) heat loss through glass can be reduced by: using double glazing – the gap
reduces loss by conduction. The types of double glazing are (in order of increasing effectiveness):
 with air gap
 with air gap and low-e coatings
 with heavy gas gap (eg argon) and low-e coatings
 with vacuum gap and low-e coatings
 3 plastic films, low-e coating, heavy gas
Effective head – RE p 150 – the height through which the water falls in a hydro station or a tidal barrage.
See also head
Efficiency – ESS p94
Generally:
Energy output
------------------- x 100
Energy input
Carnot Efficiency (see also Coefficient of Performance)
T2
1 - ------ x 100 where T1 is input temperature in K, T2 output temp
T1
Some real-world conversion efficiencies: (RE p 6)
Up to 90% - water turbine or well-run electric motor
35-40% - coal-fired power station (waste heat not used)
10-20% - typical internal combustion engine
Electric circuits – (SG 2 p50) To increase the voltage in a circuit, cells should be connected in series.
The total voltage will be the sum of the voltages of the serially connected cells. (Connecting cells in series
will not change the current).
To increase the current in a circuit the cells should be connected in parallel. The total current will be the
sum of the currents supplied of the parallel connected cells. (Connecting cells in parallel will not change
the voltage).
The power in a circuit is given by:
P =IV
The voltage by:
V = IR
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Where:
P is the power in watts
I is the current in amps
R is the resistance in ohms
V is the voltage in volts
Emissivity – (RE p29) property of a surface which denotes how much it radiates heat. “Most materials
used in buildings have high emissivities of 0.9 – they radiate 90% of the theoretical maximum for a given
temperature”.
Low-E coatings have low emissivity.
See also: U-values
Energy:
Delivered energy – defined on p94 ESS. Delivered energy is the energy which reaches the
meter of the end-user after it has been transformed by a power station or other generator and
after it has been transmitted through the grid
Primary energy – defined on p57 ESS “the total ‘energy content’ of the original energy resource”
before that energy is extracted/transformed processed. Put another way: is the starting point for
an energy transformation system: the incoming ‘amount we have to work with’ before it is acted
upon by power stations
Somewhat arbitrary - uses conventions (p65-66) which need to be understood.
T206 conventions taken as (except where stated otherwise): Notional primary energy for all types
of power station except hydro = electrical output  0.33. Notional primary energy for hydro is just
the electrical output. Bear in mind when comparing nuclear with hydro. Also a question of how
the other renewables are treated.
Useful energy – the energy that finally emerges (at the end of an energy transformation
sequence) to perform the service that we want. (For example the energy emitted by a light bulb)
Energy balance – see energy payback ratio
Energy crops – RE p113 – plant biomass intentionally grown as an energy carrier. Examples are:
Fast growing trees eg willow, hazel
Miscanthus – a C4 grassy plant
Energy-from-waste (EfW) – RE –125 – refuse incineration with heat recovery
Energy payback ratio/energy balance/energy ratio – ESS p558 – the ratio of energy generated over
the lifetime of a power plant to the energy required for its construction and maintenance. Also known as
Energy returned on energy invested or EROI
ESS quotes a study which gives the following payback ratios:
Nuclear – 16
Wind – 80
Coal – 5-7 (depending on whether SO2 scrubbing included)
CCGT – 5 (including gas transmission over 2000 km)
PV – 9 (currently – expected to drop)
Biomass - 5
EROI (energy return on energy invested) – see Energy payback ratio
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Feed-in law – RE vid – a possible way of encouraging uptake of photovoltaic and other renewables,
pioneered in Germany. The principle is that a higher price is paid for electricity from PV sold to the grid for
a fixed no of years (20 in the German example). The higher price declines with each year to discourage
waiting (declines by 5% in the German example. Strictly, this is not government subsidy, but subsidy by
other electricity purchasers.
See also Renewables obligation, which is the mechanism favoured by the UK government.
Fertile – an isotope is fertile if it can become a fissile isotope after the absorption of a neutron. For
example U-238 in the following reaction:
238 239 - 239 - 239
92U + neutron ----> 92U -- 23 minutes----- > 93Np -- 2.3 days----> 94Pu
A uranium-238 nucleus absorbs a neutron, becoming a uranium-239 nucleus. Uranium-239 is unstable
with a half-life of 23 minutes. It decays by - radiation, i.e. one of its neutrons decays into a proton and
an electron. A different number of protons means a different element – Neptunium-239. This element is
subject to the same process (though with a half-life of 2.3 days) and one more proton gives the element
plutonium-239
Fisher-Tropsch synthesis – an indirect liquefaction method of coal liquefaction. Indirect because the
first part of the process is Lurgi gasification (producing syngas).
Fissile – an element is fissile when its nucleus is liable to spontaneously fission giving rise to two
daughter nuclei plus some free neutrons. Uranium-235 is effectively the only naturally occurring fissile
element. Plutonium-239 a product of the radioactive decay (rather than fission of U-235) is also fissile
(and there might be a very small amount of that which is not man-made as a consequence of the Oklo
‘natural reactors’).
Fission – (ESS ch 10) the splitting of a nucleus giving rise to two daughter nuclei plus some free
neutrons.
Fission results in a slight loss of mass which appears as energy. The energy released in the complete
fission of 1 kg of U-235 is equal to that released in burning about 3000 tonnes of coal (ESS p404)
See also chain reaction and fusion.
Flat bed water collector – (RE) a type of solar (active) heating device. A ‘sandwich’ of glazing and
black ‘absorber plate’ with a ‘filling’ of tubes through which water runs. The water absorbs the solar
energy and heats up. In a building, these are typically roof-mounted. Because they are easily scalable,
some useful heat can be collected even in quite small systems and they could make up to some extent
for poor insulation.
Flue Gases – ESS p181 Gases emitted during coal combustion and lost in the flue. P181. These are in
order of amounts (largest first):
Nitrogen
Carbon dioxide
steam
NOx see chemistry notes
SO2 See flue gas desulphurisation in chemistry notes
Fly ash aka particulates
Flue Gas desulphurisation (FGD)– ESS p181, 182. A process to remove sulphur from flue gases by
using limestone. One way of doing it:
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SO2 + CaCO3 --> CaSO3 + CO2
Fluidized bed combustion (FBC) – ESS p179. Process used in modern coal-fired power stations.
Principles are:
 Thick layer of sand or gravel (i.e. inert) particles of 0.3 –2.0 mm on a base plate
 Base plate has apertures through which air is blown
 At certain speed the material expands and behaves like a liquid …
Types are (in order of ‘conventionality’):
 Bubbling fluidised bed combustion
 Circulating fluidised bed combustion
 Pressurized fluidised bed combustion
Fossil Fuel (ESS p 157) – fuels which are derived from ancient living matters, vegetable or animal, which
have undergone chemical changes.
Fossil Fuels, improving (ESS p 537). The ways to do this are:
 Improve energy conversion efficient, for example:
o CCGT
o CHP
o High efficiency condensing boilers
o Higher efficiency engines
 Clean up fossil fuel combustion
o Techniques for removing SO2 NOx (such as flue gas desulphurisation)
o Using less carbon dense fuels (such as methane)
o Carbon capture & sequestration
 Fuel cells
Four stroke petrol cycle – (ESS p277) Sequence of events is:
 Induction – fuel/air comes in. Piston descends
 Compression – fuel inlet closes. Piston rises
 Ignition – spark! Piston descends
 Exhaust – exhaust gases out. Piston rises
See also diesel engine
Francis turbine – see turbines, hydro
Fuel cell – (ESS p584 RE p408) a ‘gas battery’, which produces electrcitiy by a sort of reverse
electrolysis: oxygen and hydrogen are fed in and electricity and water come out.
Fuel cells generate electricity by combining a reactant which is oxidising with one which is reducing. The
reactants are most usually hydrogen and oxygen (a ‘reverse’ electrolysis) in which case the only
emissions are water and a little heat. As a fuel cell is not a heat engine its efficiency is not limited by
Carnot’s law.
Efficiencies are ‘currently in the range 40-60%, which makes the ‘hydrogen bus’ viable, but for non-
transport applications is only competitive with a CCGT (45-55%).
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Furans – mentioned on p535 as related to Dioxins, but otherwise not mentioned further
Fusion – (ESS p 429). The process of two lighter nuclei joining to form one heavier one
Future discount rate – (ESS) a financial analysis device which takes account of the fact that money
which one expects in the future is for various reasons ‘worth less’ than money which one actually has
now. (There is a sense in which the future discount rate quantifies impatience – if you want a quick return
you will assign a high discount rate).
Types of generation can differ in cost per kWh depending on the choice of discount rate. High discount
rates favour plant (such as CCGT) with low capital cost and which are quick to build regardless of fuel
cost and lifespan. It takes a low discount rate to turn the lifespan of big hydro or the low fuel costs of
nuclear into a favourable cost per unit of electricity.
See also PMT.
Gasoline Direct Injection (GDI) - (MTE) improved internal combustion engine design. As the name
indicates, this dispenses with the carburettor stage, where air and petrol are mixed, by directly injecting
petrol into the combustion chamber. An increase in power (hence more km for the carbon emitted) occurs
because this process causes a ‘cleaner’ burn, hence reduction in CO 2 emissions for distanced travelled.
See also lean burn
Glass – (RE p26) Glass is transparent to visible light and short-wave infrared radiation, but opaque to the
long-wave infrared radiation re-radiated by the surface behind it – hence ‘the magic of glass’. There are
some plastics which have similar properties. The transmittance (amount of light which passes through) of
glass can be improved by minimizing the iron content.
Greenhouse gases – ESS p539, 540, 541 – These are:
 Carbon dioxide, CO2 – the most important greenhouse gas implicated in global warming
increased from 285 to 370 ppm since 1850;
 methane, CH4 estimated to have increased 145% since 1850;
 Dinitrogen oxide N2O(aka nitrous oxide), - estimated to have increased 14% since 1850 – see
also NOx
 halocarbons (which include cfc’s); entirely anthropogenic and emitted in relatively small quantities
 Ozone O3; estimated that the warming effect of ozone in the troposphere is greater than the
cooling effect of ozone depletion in the stratosphere
 Water vapour; - most important (?) for the natural (non-anthropogenic) greenhouse effect, but
also acts as a positive feedback for anthropogenic warming
Grid – electricity distribution system in which generating plants share, and are shared by, a common
distribution infrastructure. To make this work you need: single frequency AC (50 hz in UK and Europe)
and ways of dealing with fluctuations in demand to maintain this frequency. Methods for balancing the
grid:
 Grid strengthening – links to other countries can export surplus, import deficit – UK already has
one to France
 Peaking plant and big hydros – can comes on line rapidly for sudden increase in demand
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 Spinning reserve – plants kept generating at part-load which can increase production suddenly –
but inefficient
 Pumped storage – when there is too little demand, water can be pumped uphill in certain hydro
systems as a way of storing the energy
 Offering off-peak prices for electricity (see RE fig 10.17 for French example)
 Demand management – undeveloped as yet, but many applications not time-critical and could be
fitted with devices which respond to state of grid
This is highly relevant to the increased use of renewables, as there may be integration issues.
Half-life – (ESS) the amount of time which it takes a radioactive element to halve in mass via radioactive
decay. If you have m mass of radioactive element x which has a half life of t, then
after t you would have m/2
after 2t there would be m/4
n
after 3t there would be m/8 … after nt there would be m/2
HAWT – horizontal axis wind turbine
Head – RE p162 - the distance through which water falls in a hydro system (or barrage). The (loose)
classification is as follows:
 Low – ‘less than perhaps 10 metres’
 Medium – in between the other two
 High – ‘appreciably more than 100 metres’
The available head determines the type of installation – but the above heights are not to be taken too
rigidly:
 Run of river – these will have a large volume flow, but a slow one
 ‘medium head’ – these type often have a very high dam (eg grand coulee – 170 metres) but the
penstock is relatively short (diagram RE p162)
 ‘high-head’ - are distinguished from the above type by the fact that t’the entire reservoir lies well
above the outflow level
See also turbine, types of, as choice of turbine is closely related to head.
Heat exchanger – (ESB p26) used in a Mechanical ventilation with heat recovery system, this unit
can be one of two types:
 a multiple layer of thin,. flat, metal plates with incoming and outgoing air passing through
alternate layers. This gives a large area of metal through which heat can .flow.
 alternatively, two quite separate heat exchangers use water as the heat transfer medium, which
is pumped between them in run-around coils
Heat loss – (ESB)
 Fabric heat loss -via the walls, windows, roof and floor (see heat loss coefficient). Ways of
reducing:
o Low-E coating for glass
o Double glazing
o Cavity walls (though beware of thermal bridges)
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 Ventilation loss - via exchange of air with the outside environment. Some ventilation loss is
necessary and designed-in, but there can also be unintended heat loos via gaps and cracks in
the fabric (one design option is ‘super insulation’ which requires mechanical ventilation with
heat recovery)
Heat loss coefficient – (ESB p21) Total fabric heat loss from a building, Qf is the sum of all the U-values
of the elements of the external fabric (walls roof, floor, windows, doors) multiplied by their areas,
multiplied by the inside-outside temperature difference:
Qf =  (Ux x Ax) x T
Heat pump/refrigerator - ESS p364 Essentially these are the same machine. It exploits two
thermodynamic properties of matter: (1) energy is needed for a phase change, so a large amount of
energy is absorbed as a liquid evaporates and (2) the higher the pressure, the higher the boiling point.
Both fridge and heat pump make use of an evaporator and a condenser, linked by a compressor which
provides the external work input. Using the physics distinction between system and environment, in a
fridge the evaporator is within the system – the bit you’re interested in – while the condenser is in the
environment – the rest of the world which is not your focus of current interest. In a heat pump their
positions are reversed.
Starting from the evaporator stage of the cycle, the refrigerant (which needs to be a substance with a
relatively low boiling point) evaporates and absorbs energy (property (1), as above). Temperature is
lowered (the function of the machine in a fridge, of no interest in the heat pump). The vapour passes
through the compressor which returns the refrigerant to the liquid phase, so it gives up energy (warms the
kitchen with a fridge, does the job in the heat pump). The liquid is now returned to the evaporator –
where it loses pressure and so evaporates (property (2) as above).
Heavy oil – see non-conventional oil
Hot dry rocks (HDR) – a geothermal energy source.
Human disruption index (HDI)– ESS p520 – the ratio of the human-generated flow of a particular
substance to its natural (‘baseline’). The HDI was invented by Holdren & Smith (2000) – reference on p
567 of ESS.
Hydro electric power – (RE p156) The power supplied by a hydro electric installation is given by:
P = 1000 x Q x g x H where
P is the power in Watts
Q is the flow of water in cubic metres per second
H is the height through which the water falls
3
(1000 is the mass in kg of 1m of water)
Hydrogen economy – (RE, ESS, MTE) Hydrogen is the most common element and easily available
(though bound up in water or hydrocarbon molecules). Burning hydrogen has the advantage of CO 2
emissions. The ‘hydrogen economy’ is the idea that it would be possible to run world’s energy system
using hydrogen as its main fuel, particularly as one of the inputs to fuel cells. The hydrogen would be
generated from renewable resources, thus eliminating carbon altogether.
There are a number of practical difficulties in developing such a system, even apart from the prerequisite
development of renewables:
 Significant infrastructure does not as yet exist. In particular if hydrogen is to be used in vehicles,
a network of filling stations is required. There is no incentive to create one until there is a
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Martin Parkinson’s T206 Glossary
customer base of hydrogen vehicle owners yet there can be no marketing or development drive
to create a customer base until there are filling stations.
 For transport usage there are storage issues. : H2 has a high energy content by mass but a low
one by volume. So to store as a gas requires compression. Storage as a liquid requires
refrigeration. A third method involves storing it in the form of metal hydrides. All three methods
add to costs and are not yet fully developed.
Current development timescale estimates are in decades rather than years.
Illuminance - (ESB p52). Amount of light falling on a given surface. Unit is the lux
Impacts – ESS p 520 – the potential results of an energy system. Distinguish from insults.
Infiltration – (ESB p23). Undesigned and uncontrolled ventilation. Air flow through gaps and cracks in a
building
Inflation – ‘decreases purchasing power of money in real terms’ over time. Defined as: ‘Rate of change
of the retail price index per year’
Integration – (RE ch 10) renewable sources (apart from biomass) can be unpredictable and/or
intermittent and this presents a problem for their integration into a grid system which has to maintain a
balance of supply and load on a moment to moment basis. It is sometimes argued that renewable
sources can never be more than a minor player in the ‘mix’ for this reason, because they will require
wasteful amounts of peaking plant and spinning reserve, but the position is more hopeful than that (even
apart from grid connections to other countries).
Wind & wave - Many sources smooth out supply, in the same way that demand is smoothed out
over many small loads. A dead calm over the whole of the UK is rare. Denmark has had the
experience of too much wind energy: ways of dealing with this can be at the level of the turbines
themselves, or dumping the power as heat. Wind and wave have advantage that main production
(winter) tends to coincide with heavy demand.
Tidal stream – fairly predictable but intermittent. Turbines will generate at different times
according to location and so could be planned to provide a continuous source
Tidal barrage, lagoon – intermittent but predictable so much less of an issue than wind or wave.
Double and triple-basin systems could ensure a fairly continuous supply
Photovoltaic – unpredictable and in the UK main production (summer, daytime) is time of lowest
demand. Storage system is needed.
Inverter – device for turning DC current into AC current which can therefore be fed into the grid.
IGCC, integrated gasification combined cycle - (RE p 591) Type of ‘clean coal’ generation plant. The
design is related to that of the CCGT in that it has a gas turbine, the output of which then heats water for
a steam turbine. However there is a preliminary stage in which coal is gasified and the syngas ‘cleaned’
(see FSG) – CO2 can also be removed and then sequestered.
Insolation – amount of solar radiation. More specifically, the rate at which energy is delivered at any one
-2
time, to a horizontal surface, so unit is usually W m . A second meaning is the energy delivered over a
-2 -1
given period, so this will be kWh m d - kilowatt hours per square metre per day or year (RE study guide
p20)
-2
The maximum insolation, sun overhead and before absorption by the atmosphere is 1380 W m
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Martin Parkinson’s T206 Glossary
Insult – ESS p520 – physical stressors (such as air pollution) produced by an energy system. Contrast
with impacts of the system.
Integrated gasification combined cycle (IGCC) – (ESS p591) ‘one of the most promising approaches
to reducing emissions from coal-fired electricity generation. Syngas produced from coal is bunred in a
combined cycle gas/turbine/steam turbine similar to that of a conventional CCGT … because energy is
required to convert the coal to syngas, the overall efficiency .. is around 45%’
‘…sulphur and nitrogen compounds can be removed from the gas before it enters the turbine … carbon
dioxide is produced during the reformation process ..[but] .. it is relatively easy to capture …’
Kerogen – see non-conventional oil.
Landfill gas (LFG) – ESS p74 – the organic component of the waste in landfills decays in the absence of
air (anaerobic digestion)to produce a gas that is relatively rich in methane. since the start of the 90’s this
has been increasingly collected and used, mainly as a fuel for small scale electric power plants.
o.
Latitude, seasons and insolation – (RE study guide p36) The axial tilt of the earth is 23.5
Consequences of this are:
Latitude of the tropics is the same as that of the tilt
o o
Latitude of the Arctic/Antarctic 90 minus the tilt = 66.5
o
Solar altitude at noon at the equinox = 90 – the latitude
o
Solar altitude at noon at midsummer = (90 – the latitude) + the axial tilt
o
Solar altitude at noon at midwinter = (90 – the latitude) - the axial tilt
Lean burn engine – (ESS) An internal combustion engine in which the air/fuel ratio has been reduced to
around 20:1. Although ‘weaker’ (starting at a ratio of 16:1) air-fuel mixtures burn at a higher temperature
(thus tending to produce more NO x) at 20:1 the combustion process is too fast for any NO x to be
produced. Lean burn engines are also more efficient, and have lower hydrocarbon and CO emissions.
However, lean-burn engines need careful design.
See also catalytic converter
Limpet – a type of oscillating water column – see wave devices
Load factor - ESS p353 similar to capacity factor but strictly speaking refers to the demand rather than
the output of generator which supplies it. RE p220 – ‘in effect the percentage of time the plant can deliver
power’. Some comparative annual load factors are:
A typical nuclear station 77%
A typical CCGT 84%
Estimate of the Severn barrage 23%
Low-E – see Emissivity
Lumen – (ESS p 103) Unit of perceived light intensity (“…a unit of light energy …which uses the human
eye as the meter”). Some examples are:
Modern 100W filament lamp – 1400 lm
Wax candle – 13 lm
Reasonable standard for desk lighting – 300 lm
See also Lux, Luminous efficacy etc
-
Luminous Efficacy - (ESS p104, ESB p50). Effectiveness of lighting systems in lumens per watt (lm W
1
).
Luminous flux – (ESB p52). Flow of light emitted by a lamp
15
Martin Parkinson’s T206 Glossary
Lux – (ESB p52). Unit of illuminance. One lux is defined as a luminous flux of 1 lumen falling on an
2
area of 1 m .
Mechanical Ventilation with Heat Recovery (MVHR) – (ESB p25) a method of reducing the heat loss
doe to ventilation in buildings. The warm outgoing air pre-heats the cold incoming air by passing both
streams through a heat exchanger. Requires a properly airtight building to work effectively.
Advantages: controllable ventilation, adjustable to each room
Disadvantages: requires complex ductwork and air pumping which can require large amounts of electrcity
Moderator – (ESS ch 10) material in a nuclear reactor which acts to slow down free neutrons so that they
are more likely to cause fission and hence maintain the chain reaction. A moderator will be an element
with a low atomic weight – collision of a light object with one much heavier will not slow it down much.
In some reactor designs a liquid moderator (such as heavy or light water – with deuterium or normal
hydrogen) also serves as the coolant. The most common non-liquid moderator is graphite.
Money – ESS p483 - has 3 functions: medium of exchange, unit of account (enabling us to talk about
value) and a store of value over time.
MOX (mixed oxide) – (ESS ch 10) nuclear fuel which is a mixture of depleted uranium and plutonium
(which is the fissile material to make it work)
Municipal solid waste (MSW) – basically household waste. ESS p21 RE p120, 130, 142 dealt with in 3
possible ways:
 Landfill – with possible recovery of landfill gas,
 Combustion – with possible use of heat, as heat or for electricity generation
 Anaerobic digestion - produces biogas, which can be used as above. Digesters for MSW use
the organic fraction of the waste diluted into a slurry, with possible addition of sewage
ESS p 21, concerns over possible emissions of dioxins during combustion. RE p 126 – Moisture content
tends to be at least 20%, energy density about a thirteenth that of coal. See also refuse derived fuel.
Non conventional oil/petroleum – (ESS p278) Crude oil produced from other sources than
conventional oil and also of conventional sources recovered by tertiary recovery. Examples are:
 Oil shale – sedimentary rocks which contain the waxy solid kerogen
 Tar sands – loose grained rock bonded together by heavy bituminous material
 Heavy oil – buried, highly sulphurous petroleum deposit which will not flow to the surface under
natural reservoir pressure
There a vast non-conventional oil resource (US and Australia for kerogen, Canada and Russia for tar
sands, Venezuela for heavy oil) but it is energy intensive to exploit and therefore currently uneconomic.
The environmental impacts are also severe. It will only become significant if hydrocarbons are still a
dominant energy source by 2050 (ESS p282)
In 2003, 0.05% of world oil production was non-conventional.
NOx – ESS p 175, 531 – Generic term for the Oxides of Nitrogen – respiratory irritant and contributor to
acid rain (nitric acid, HNO3). The inevitable result of burning any fuel in air. Main source is internal
combustion engine.
NO – nitrogen oxide or nitric oxide
NO2 – nitrogen dioxide
N2O – dinitrogen oxide or nitrous oxide (see also greenhouse gases)
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Martin Parkinson’s T206 Glossary
NOx can be emitted if there is nitrogen in the fuel. Most common cause is ‘thermal’ – oxygen and nitrogen
in the air combine at high temperatures of fuel combustion
o
> 1500 C N2 + O2 - 2NO
the temperature must be this high for a certain amount of time
as this cools 2NO + O2 - 2NO2
Photochemical smog:
NO + 2O2 + sunlight -- NO2 + O3
Nuclear contribution – (ESS ch 11) around 6% of the world’s primary energy – about 17% of world’s
electricity. 439 plants in 2003. Top 3 nuclear nations are France, Lithuania and Belgium who each obtain
more than half their electricity form nuclear. In 2006 (see figure 1) 18% of UK electricity was nuclear
generated.
In regards to CO2, nuclear generation produces one tenth as much per kWh as CCGT, (0.05 kg as
against 0.5 kg – a modern coal plant produces 1.1 kg)
Nuclear economics – (ESS p442, 464).
 High plant cost - typically 3 times the cost of fossil fuel plants. Mainly because of need to use
special materials and safety features.
 High operating and maintenance costs – again, around 3 times those of fossil fuel.
 High or unknown decommissioning costs
 Low fuel costs – fully fabricated fuel 20% of overall generation cost, about one third of that for
coal plants. 1 kg of natural uranium contains the 20 000 times the energy of 1 kg of coal
‘The crucial prerequisite of a revival of nuclear power would be an improvement in the economics’
 Improve operational efficiency – has already happened in Uksince privatisation
 New technology – Improved PWR, PBMR
Nuclear fuel cycle – (ESS ch 10)
 Mining – natural uranium only weakly radioactive, but hazard from radon
 Extraction – rock crushed, dissolved in H2SO4 and recovered as yellowcake. ‘Tailings’ from the
extraction process can be twenty times as radioactive as the uranium and require safe storage.
 Enrichment – methods are either gaseous diffusion or centrifugal. Depleted uranium is by-
product, usually waste
 Fabrication of fuel elements
 Fuel element spends around 3 years in reactor. Will now contain many radioactive fission
products esp plutonium
 Disposal – at the moment this is storage of some kind.
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Martin Parkinson’s T206 Glossary
 Reprocessing – separation of spent fuel into uranium, plutonium and other wastes. Plutonium
can be used in MOX, uranium can be re-enriched.
Nuclear reactor – (ESS ch 10)
The basic parts – apart from the turbines and so on - are:
 Core, containing:
o Nuclear Fuel
o Moderator
o Coolant
o Control rods
 Containment
 Shielding
Nuclear reactor types – (ESS ch 10)
Some designs are:
 Light water Reactors (LWR) – use water as moderator and coolant. Fours fifths of reactors are
LWRs
o Pressurized water (PWR) – about three quarters of LWR’s. Fuel is uranium oxide,
enriched to 3.5%
o Boiling water (BWR) – here water is allowed to boil to provide steam for the generators.
 Gas cooled reactors
o Magnox – fuel is natural uranium metal, moderator graphite and coolant CO 2
o Advanced gas cooled (AGR) – fuel is enriched uranium oxide 2.3%, moderator graphite
and coolant CO2
 CANDU – fuel is natural uranium, moderator and coolant both heavy water
 Fast reactors – the chain reaction is maintained by fast neutrons (one which have not been
slowed by a moderator). So no moderator and more highly enriched fuel (up to 20% U-235)
because fast neutrons less efficient at inducing fission.
o Fast breeder reactor - fast neutrons more efficient at producing plutonium, so possible to
breed more fissile material than you start with.
(See Pebble bed modular reactor as an example of a new, smaller and safer design
Nuclear waste – (ESS ch10, 11). Major disadvantage of nuclear generation (others are proliferation,
expense – accidents rare but arguably of different order of risk?)
 Low level – almost 90% by volume, contribute 1% of total radioactivity. Mainly materials and
equipment.
 Intermediate level – slightly more than 10% of volume, 5% of radioactivity. Any substance in or
near the reactor core – induced radioactivity due to neutron bombardment – eg fuel cladding
 High level – most of the radioactivity and the main problem. Spent fuel and fission products
resulting from reprocessing.
Oil exploration – (ESS p)
 Gravimetric survey
18
Martin Parkinson’s T206 Glossary
 Geomagnetic survey
 Seismic survey
 Appraisal wells
 Production wells
Oil refining – (ESS p) crude oil is mixture of different hydrocarbons (different fractions) which can be
used for different purposes.
Distillation - Each fraction has a different boiling point, enabling each to be separated by a process of
heating – evaporation – condensation.
o Light distillate – BP 70-200 C includes petrol, aviation fuel, paraffin used as chemical
feedstock (naptha)
o Medium distillate – BP 200-350 C includes DERV , ‘gas oil’
o Heavy distillate - BP +350 C solid/semi-solid at room temperature. Marine diesel is on the
medium/heavy border. ‘fuel oil’ – power stations and large industrial boilers
Cracking. The lighter fractions are more in demand than the heavier ones and it is possible to split the
large hydrocarbon molecules into smaller ones. (Thermal cracking, catalytic cracking, hydrocracking)
Oil shale – see non-conventional oil
Opportunity Cost – the ‘opportunity’ is a potential financial investment. The opportunity cost occurs if
one spends money now (one incurs the cost of the profits one could have gained by investing) or by
investing relatively badly (one incurs the ‘cost’ in the form of lower profits that one might have gained)
Organic Rankine Cycle (ORC) – RE p 53 – systems which use turbines are sometimes called Rankine
systems. When using a simple solar collector it can be difficult to achieve a sufficiently high temperature
to raise steam, but there are stable organic chemicals (similar to refrigerants in heat pumps) with low
boiling points. Stem which uses an organic fluid and a turbine is an ORC. Used with solar ponds,
OTECs and geothermal plant.
Oscillating water column (OWC) – see wave devices
Ozone, O3 - (ESS p541) A gas found in stratosphere and troposphere. In the lower atmosphere it is
formed through the interaction of O2 NOx and VOCs, energized by sunlight, and is a by-product of the use
of motor vehicles. ‘It is estimated that the warming effect due to the formation of ozone in the troposphere
is greater than the cooling effect of ozone depletion … in the stratosphere’.
Besides its greenhouse action, ozone is damaging to plant and animal life and is ‘often used as a general
indicator of the level of atmospheric pollution’.
The ozone layer in the stratosphere, is naturally formed and is beneficial because it absorbs ultra-violet
radiation
Parallel connection – see electric circuits
Particulates – ESS p 531, 533 - solid particles that are small enough to float in air. In urban areas these
are mainly from vehicle exhausts. The ones that cause concern are PM10 (i,e, < 10 microns in diameter)
and consist mainly of carbon. PM2.5 (i,e, < 2.5 microns in diameter) are now considered to be more
damaging to health
Peaking plant – see base load.
Pebble bed modular reactor (PBMR) – ESS p457 – recent design of nuclear reactor. The ‘pebbles’ are
individual fuel elements, each the size of a billiard ball, where the fuel is encased in a sphere of silica.
19
Martin Parkinson’s T206 Glossary
Helium is passed through a hopper of ‘pebbles’ and goes directly to drive the turbines. Claimed
advantages are that: the reactor is small (making it easier to mass produce and perhaps giving a wider
choice of location), and that the spent fuel is already encapsulated making disposal easier and not
requiring any reprocessing. A possible disadvantage is that because there is no secondary heat-
exchange system, if a fuel element ruptures then the whole system would be contaminated. Low power
density is though to make a meltdown unlikely however.
Pelton turbine - – see turbines, hydro
Penstock – RE p163) – ‘the channel or pipe carrying the flow’ of water in a hydro installation.
Photochemical smog – nitrogen dioxide + ozone - see NOx
Photovoltaics, economics of – RE vid – a doubling in megawatts gives a 20% reduction in price
(according to Erik Lysen) . Re p96 Energy payback time is 2 – 5 years in European condtions, and
predicted to descrease to 1.5 – 2 years
Advantages of PV:
low maintenance costs and relatively long useful life
low visual intrusiveness (there are no ‘anti-pv’ lobby groups)
no increased take-up of land – in fact they occupy otherwise ‘dead’ space
perhaps increased feelings of ‘ownership’ and ‘environmental involvement’ amongst building
owners/users
disadvantages in UK situation:
The arguments against government support is that although PV is good it is perhaps not the most
suitable for the UK and therefore not the most cost effective use of taxpayers resources. The UK
has a relatively high latitude and does not have reliable sunshine. Electricity demand is highest in
the winter when the panels will be at their least productive. PV has high installation costs and
these can make the cost of electricity per unit higher than other renewables.
Photovoltaic effect – RE p66 – probably discovered by Becquerel 1839 – experimented with wet cell
and found that voltage increased when plates exposed to sunlight. Reported in a solid in 1877 –
selenium. 1883 first recognizable solar cell from Charles Edgar Fritts. Selenium cells used in exposure
meters.
PM10, PM2.5 – see under particulates
PMT – spreadsheet function which can be used to find annual repayments for an annuitized sum at a
given discount rate. Syntax for staroffice (excel the same but with commas) is: =PMT(interest rate;
number of years; present value)
See also Annuitization, Future discount rate.
p-n junction – p and n stand here for positive and negative – i.e. lack 9positive) or surplus (negative) of
electrons.
-1
Power – rate of energy flow, so Joules per second (1 watt = 1 J s ).
 Electrical power: (where I is current and V is voltage): P = VI
 Power in a hydro (where  is the efficiency of the plant, Q is the cubic metres of water per
second, H is the effective head, and g is rounded up to 10):
P(kW) = 10  Q g H
Price; Cost; Profit – for the purposes of ch 12 ESS these are defined as:
20
Martin Parkinson’s T206 Glossary
 Price – the monetary ascription of goods determined by the marketplace
 Cost – a measure of the minimum amount for what something must be sold in order for its
production to make a profit, that is to say:
 price = cost + profit
Primary energy – ESS p57 – see under energy
Primary recovery – (ESS p278) Recovery of conventional oil
Propeller turbine – see turbines, hydro
Pumped storage – see grid
Pyrolysis – literally, the breaking apart of something by fire. Slow pyrolysis refers to the traditional
method whereby charcoal is produced from wood, left to smoulder in the absence of air at about 300-500
o
C. RE p124 ‘probably the most greenhouse gas intensive [fuel cycle] in the world.
Pyrolysis normally refers to (RE p133) ‘processes where the aim is to collect the volatile components and
condense them to produce a liquid fuel of bio-oil’
Radioactivity – (ESS) ‘Radioactivity is the spontaneous emission of particles from the nuclei of atomsthe
radioactivity of a radioactive source is defined as the number of particles emitted per second by the
source (1Bq = 1 particle per second). The greater the activity the shorter the half-life.
Rate of rotation – see turbine
Rebound effect – defined p46 of ESS
Energy efficiency leads to energy savings which also result in monetary savings. If this frees up money
which is then spent on goods or services which themselves require energy, the rebound effect is said to
occur.
Reforming - (ESS p 265) ‘general class of processes involving the rearrangement of hydrocarbon
molecules that make up oil. …a whole range of different products can be synthesised.’ Currently it is the
most usual way of making hydrogen.
Refrigerator – see Heat pump
Refuse derived fuel (RDF) – RE p126 –. RDF ‘refers to a range of products resulting from separation of
unwanted components, shredding, drying and otherwise treating’ municipal solid waste. The most energy
dense of these solids is d-RDF which contains only the combustible bits and has possibly 20 times the
energy of the original waste.
Renewables – (Re p144) energy harvesting and transformation systems which use a sustainable energy
source – i.e one ‘that is not substantially depleted by continued use, does not entail significant pollutant
emissions or other environmental problems, and does not involve the perpetuation of substantial health
hazards or social injustices. In practice only a few energy sources come close to this ideal’.
In the industrialised countries (ESS p144) 7% of total primary energy comes from renewables, three
quarters of this from large scale hydro.
Renewables obligation (RE p417) - prices for electricity generated by renewable sources are
determined by the market, but electricity suppliers are required to obtain a certain proportion of their
electricity from renewable sources. Each year the proportion so required is increased towards a 10%
target for 2010
Resource size – RE p389 – the following distinctions are made in relation to renewables:
21
Martin Parkinson’s T206 Glossary
 Available resource/total resource – ‘total annual energy delivered by the source’
 Technical potential/accessible resource - ‘ the maximum annual energy that could be extracted
from the accessible part of the available resource using current mature technology’. This may
ultimately be limited by the laws of physics but there are also limitations imposed by such
practical considerations are roads and geography and institutional restrictions
 Practicable potential/practicable resource – the technical potential further reduced by including ‘
constraints on using or distributing the energy’ and ‘further limitations on land or technology use
due to public acceptability’
 Economic potential – ‘the amount of the technical potential that is economically viable’. Viability is
a function of both acceptable price and discount rate.
Retail price index (RPI) – aka ‘cost of living index’ – ESS p takes a base year and expresses this as
100. Hence if the base year is 2000, goods that cost £100 in 2000 would have cost, say, £40 in 1980 (cf
inflation)
R/P ratio – (ESS p11 )reserves to production ratio: the number of years the reserves of a resource would
last if used/extracted at the present rate. At current figures:
Coal – 200 years
Oil – 40 years
Gas 60 years
R/P figures cannot take into account undiscovered reserves, technological or economic developments.
Secondary recovery – (ESS p278) recovery of conventional oil sources enhanced by the injection of
natural gas or water into the reservoir. See also tertiary recovery.
Semiconductors – RE p67 – non-metallic materials (eg germanium, silicon) which sometimes act as
electrical conductors, sometimes as insulators. Intrinsic semiconductors are doped to produce p – type
and n- type semiconductors which are used together to create a p-n junction which is the basis of
semiconductor applications such as transistors and photovoltaics.
Serial connection – see electric circuits
Short rotation coppice (SRC) (European) Short rotation forestry (SRF) (rest of world) – RE p114 -
system of growing woody biomass where harvesting takes place every 3-5 years for up to 30 years.
Significant wave height – (RE p305) figure used to calculate wave power. It is 4x root mean square of
water elevation. It is approximately equal to the average of the highest one third of the waves – and
generally the estimate of amplitude made by eye.
Solar heating, Active – RE p 18 – in contrast with passive solar heating, active systems involve the use
of a separate or separable solar collector to gather solar radiation. Usually a simple device and the heat
o
at below 100 C. See Flat bed water collector and solar water heater as examples and do not confuse
with Solar thermal engine.
Solar heating, Passive - the absorption of solar energy directly into a building to reduce the energy
required for space heating. Really applies to systems where the collector and heat store are integral
parts of the building using architectural features which exploit solar energy – walls windows and so on
can be designed to make the most of sunlight, but they are also necessary for the building. See Trombe
wall as an example.
Sometimes used more broadly to mean the whole process of integrated low-energy building design.
There a 5 broad rules for optimising use of passive solar heating in buildings: (RE p45)
22
Martin Parkinson’s T206 Glossary
1. good insulation
2. Responsive, efficient heating system
3. South facing, with glazing concentrated on the south side as should the main living rooms
4. Overshading avoided
5. ‘thermally massive’ to avoid overheating in summer.
Solar thermal engine/Solar electricity generating system (SEGS) – RE p54- 58
 Power tower – or central receiver system – uses a field of tracking heliostats, reflecting the sun
onto a boiler at the top of a central tower.
 Parabolic trough concentrator – rays are concentrated on a pipe running the length of the mirror.
Pipe contains a heart transfer fluid, heat exchangers raise steam to drive turbines. Can achieve a
concentration ratio of over 1000
 Parabolic dish concentrator – here the engine itself (often a Stirling engine) is at the focus of a
parabolic mirror
 Solar pond – large salty lake is used as a kind of flat-bed collector. Hot salty water at the bottom
o
cannot rise, upper layers of water at as insulator, bottom of the pond can reach 90 C which can
run an organic rankine cycle
 Ocean thermal energy conversion (OTEC) – uses the temperature difference between surface
o
and depth of the sea which can be 20 C in waters > 1000 m. Still very experimental
 Solar chimney – warm air produced in large greenhouse rises through a tall chimney creating
updraft which drives an air turbine at its base.
Solar water heater – (RE p19) A domestic pumped solar water heater consists of 3 basic parts:
2
Flat bed collector – typically 3-5 m mounted on roof
Storage tank – typically 200 litres, possibly the normal hot water tank, usually contain immersion
heater for winter, usually insulted. Hot water from the collector circulates through heat exchanger
at bottom of tank
Circulation system which pumps hot water from the collector to the store. Circulation water
usually contain an antifreeze in n Europe.
Specific latent heat of vaporization - defined ESS p173 - The energy needed to evaporate 1kg of any
liquid
Specific heat capacity - defined ESS p137. The heat energy needed to raise the temperature of 1kg of
o
any substance by 1 C
Spinning reserve – see grid
Stirling engine – ESS p 322 RE p56 – type of (characteristically quiet and smooth) external combustion
engine, invented 1816, which exploits heat difference. Steam engines have difficulties working at
o o
temperatures greater than 700 C, but stirling engines can go up to 1000 C hence potentially more
efficient and hence often used with parabolic dish solar concentrators (see Solar engines).
Sulphur dioxide (SO2) – ESS p 531 – produced by the combustion of almost any fuel – both biofuels
and fossil fuels contain some sulphur in varying amounts. The proportions differ as do the ease of
removing the sulphur. Coal-fired power stations are the main producers. SO2 converts to H2SO4 in the
atmosphere. The main contributor to ‘acid rain’. Can produce an aerosol.
23
Martin Parkinson’s T206 Glossary
All coals contain sulphur – up to a max of 5% by mass.
Can be removed from flue gas by introducing limestone (CaCO3) into furnace (see Flue gas
desulphurisation)
Sustainability – ESS p6. In general: meeting the needs of the present without compromising the needs
of future generations (taken from the 1989 UN Brundtland commission). With regard to energy,
sustainability is defined by ESS as the harnessing of energy sources:
 Which are not substantially depleted by continued use
 Which do not entail the emission of pollutants or other hazards to the environment on a
substantial scale
 Do not involve the perpetuation of substantial health hazards or social injustices
Syngas/synthesis gas/water gas - mixture of carbon monoxide and hydrogen (and possibly a little
methane). Defined in RE p127 as ‘a mixture of CO and H2 from which almost any hydrocarbon, synthetic
petrol or even pure hydrogen can be made’. See also town gas
Tandem compound – see turbine
Tapchan – see wave devices
Tar sands – see non-conventional oil
Tertiary recovery – (ESS p278) Recovery method for conventional oil deposits in which high pressure
steam is used to extract some of the 50% of the resource left behind by primary and secondary
recovery. Oil thus recovered is usually classified as non-conventional.
Thermal bridge – any structure (ducting, structural elements such as steel joists and so on) which
traverse the wall of a building and provides a pathway for heat loss by conduction.
-1 -1
Thermal conductivity – (ESB p15) a property of a material, usually denoted as k, in units of W m K .
That’s to say the rate of heat flow (in watts) which would flow across a one metre cube of the material
with a temperature difference of one degree (K or C).
Heat flow per square metre of area
k = --------------------------------------------------------------------
temperature difference per metre of thickness
See also heat loss.
Thermal resistance – (ESB p 21) is related to thermal conductivity, but in necessary for making
calculations about real or hypothetical buildings – hence the formula includes the t, the thickness of
2 -1
material in metres. Unit is m K W
t
R = ------
k
Where t is thickness of the material in metres, and k is thermal conductivity in watts per metre per Kelvin.
2 -1
Unit is m K W
See also U-value because:
1 1
R = ------- and U = -------
U R
24
Martin Parkinson’s T206 Glossary
The total thermal resistance of a wall is the sum of the resistances of the layers of the wall:
R total = R outside surface + R1 + R2 …+ R n ….+ R inside surface
Tidal barrage –
Theoretical maximum energy, E, that can be stored in one tidal cycle (where  is the density of water, A is
the surface area of the basin, R is the tidal range and g is gravitational acceleration):
E = 0.5  A R g
2
Tidal energy – single v double basin - The tide cycle gives two high (and low) tides within each 24-hour
day. Because tidal generation depends on there being a difference between the water level stored from
an earlier part of the tidal cycle and the ‘natural water’ level, generation can only take place at certain
times in a single-basin system. The tides are spaced slightly more than 12. hours apart so the timing of
the tides will change progressively throughout the lunar cycle which is responsible for the basic cycle..
In a double basin system there are two reservoirs and therefore can have further generating periods
within the day.
Tidal stream - Tidal stream systems harness the horizontal kinetic energy of the tides to drive turbines
which are submerged in the sea, either anchored to or rooted in the seabed.
Input power, P, reaching a tidal stream turbine (where  is the density of water, A is the area swept by the
tubine, and v is the velocity of the water):
P = 0.5 Av
3
(this is essentially the same as the formula for wind power)
Time preference for money – all things being equal, it is better to have money now than in the future. If
payment is deferred that money must include compensation for forging the use of it now. It is time
preference that determines interest rates. Present value = future value + interest
Time value of money - ESS ch 12 – the value of money is dependant on when that money is available.
The mechanisms involved are: inflation, time preference for money and opportunity cost.
Topping cycle – (ESS p 381) the gas turbine part of the CCGT cycle
0
Town gas – (ESS) Gas produced by heating coal in the absence of air to 800 C. It’s a mixture of H2, CO
and CH4 and was generated in local ‘gasworks’ and used for domestic purposes from mid-nineteenth
century (?) until replaced by Natural gas in the early seventies(?). See also Synthesis gas.
Traditional biomass – (RE p106) ‘material such as firewood, rice husks and other plant and animal
residues’ which are burned to produce heat (contrasts with ‘new biomass’). Amounted to 11.3% of world
primary energy consumption in 2000 (ESS p67).
‘Itr is estimated that traditional biomass will remain the the sole domestic fuel for over a quarter of the
world’s population in 2030’ (IEA quoted RE p144)
Transmittance – RE p26 – fraction of incident radiation which passes through a given transparent
medium – hence ‘solar transmittance of float glass’ or ‘long wave infrared transmittance of perspex’
Transport, the problem – (MTE ch 1)
For the world as a whole:
25
Martin Parkinson’s T206 Glossary
 ‘…[current trends suggest] that CO2 from personal transport could increase to more than three
times the current levels within 20 years’ .. although … long-term availability of oil problematic
 ‘current growth trends in car use seem to be both economically and environmentally
unsustainable’
For the UK:
 ‘The amount of CO2 generated by transport … has doubled in the last 25 years and is the fastest
growing source of all emissions’
 ‘road transport CO2 emissions steadied in the 1990s [ enhanced design] but have now started to
rise again … the dft predicts … increase …’
 ‘Fuel consumed by motor vehicles is about 80-90% of total life cycle energy consumption’
 ‘about 80% of of transport energy in the UK is consumed by motor vehicles, and three quarters of
that is by cars’ (i.e 60%).
 (RSS p116) percentage delivered energy to the transport sector (2000): 34% (19% in 1970)
 20% of CO2 emissions (MTE p51)
Transport, the possible solutions – (MTE)
 Less carbon intensive fuels
 More efficient vehicles (so using less of those better fuels for the same distance)
 Reductions in journey length/journeys per person
Trombe wall – (RE p34) architectural feature which is also a solar (passive) heating system. An outside
wall is covered with glazing, leaving a thin space between it and the wall. The wall acts as the thermal
storage. To be most effective the wall should be large and receive plenty of solar radiation – thus
interfering with light reaching the inside of the house. For this reason trombe walls are most suitable for
larger buildings (allowing enough natural light from windows in the other walls) or in sunnier climates
(where one might not want too much sunshine in the building, and where the wall can be smaller).
Turbine
General principles – device which transforms kinetic energy into rotary motion which then can
drive a generator. Numerous designs – some of which utilise a set of fixed guide vanes, which
direct the fluid onto the moving runner blades.
Cross compound / tandem compound - ESS p216 - alternative arrangements of a set of turbines
in a power plant. In a tandem compound arrangement, the turbines drive one rotor. In the cross
compound they drive 2 at different speeds. ‘Compound’ refers to the fact that at each set of turbs
the jet is split.
Rates of rotation – RE p151 – these are dependent on the frequency of the grid and in the UK’s
50 Hz grid will always be a sub-multiple of 3600 rpm
Ref Turbine rotation speed, this should be based on
3000 for 50 Hz (50hz x 60 secs = 3000 rpm) or submultipes
for other generators, eg 1500 for a 4 pole geni.
Turbines, hydro – (RE ch5) – the broad division of types of turbine used in hydro installations is:
26
Martin Parkinson’s T206 Glossary
 Reaction turbines – use guide vanes to direct the flow onto the runners and it is the reaction force
which transfers energy to the runner and maintains rotation. Reaction turbines run fully
submerged with a pressure difference across the runner
 Impulse turbines – do not use guide vanes, the flow moves the turbine directly – hence ‘impulse’.
Rather than being fully submerged they are driven by a jet of water and so are ‘essentially
operating in air at normal atmospheric pressure’
Some specific hydro turbine designs are:
 Francis – reaction turbine, the most common type in medium-large scale plants. Head range 2-
300 m. In a Francis turbine, (which is submerged in water) water enters directed by a curved
channel and leaves from the centre of the turbine in the axial direction.
 ‘Propeller’ – extreme form of the francis design, the type most commonly used in low head
situations
 Pelton wheel – impulse turbine - ‘essentially a wheel with a set of double cups .. mounted around
the rim’. Driven by a high speed jet of water. In a Pelton wheel, (which is not submerged in
water) the water comes from a directed jet, hits the cups of the turbine but does not travel
‘through’ the turbine
 Turgo – impulse turbine, a variant on the pelton
 Cross-flow – impulse turbine
Turbines, wind – (Re p252). Basic division of wind turbines is into horizontal axis (HAWT) and vertical
axis (VAWT).
HAWTs divide into high solidity (large number of blades), often used to drive a pump (high starting
torque), and low solidity where the rotors resemble aircraft propellers (one, two or three blades).
VAWTs can harness winds from any direction without the need to reposition the rotor.
Turgo turbine– see turbines, hydro
UK situation – (ESS p116) (see also dash for gas).
Increase in delivered energy from 1970 to 2000:
Transport +96%
Industry -42%
Domestic +27%
Service +18%
Overall +10%
Uranium – (ESS ch 10) Uranium-235 is the only naturally occurring fissile material. It is a fairly common
element, occurring in rocks and ocean, as a mixture or uranium oxides (U3O8). Urnaium bearing rock
counts as ore if it ‘contains an economically recoverable concentration of uranium’ . At present a high-
grade ore would have a few per cent U3O8, and the lowest grade would be about one part in a thousand.
Natural uranium – uranium with the ratio: U-238 of 99.27% U-235 0.72% U-234 0.0007%
Enriched uranium – has a higher proportion of U-235
Depleted uranium – has a lower proportion of U-235
Useful energy – see under energy
27
Martin Parkinson’s T206 Glossary
U-value – RE p 29 – a specification of the heat-loss performance of a building element. Defined as:
Heat flow through one square metre = U-value x temperature difference
-2 o -1
U-value units are W m C . The lower the U-value the better the insulation performance.
See also Thermal resistance
Vapour – ESS p531 – a gas at a temperature at which it can be liquefied under pressure. CF Mist,
Aerosol
VAWT – vertical axis wind turbine
Ventilation – (ESB p24). The average rate at which air flows through a building. Normally specified as
the number of complete air changes that take place in on hour, so uses the unit ACH – air changes per
hour.
See also infiltration.
VM (Volatile matter) – ESS p172 – range of gases evolved in the combustion of coal arising from the
dissociation of the coal structure. VMs carry most of the hydrogen and oxygen in the coal, some of its
carbon. VMs consist of CO,C4 and other hydrocarbons – the ‘bitumens’
VOC’s (Volatile Organic Compounds) – ESS p532 – a range of chemical compounds of different kinds
and from different sources. Include hydrocarbons, mainly resulting from incomplete combustion in internal
combustion engines, and vapours from solvents and similar materials. Many are carcinogenic and
contribute to ’chemical smog’ of urban areas.
Water gas – see syngas
Wave devices – some of these are:
Shore based:
Tapchan – tapered channel
Limpet – design of oscillating water column (OWC). Waves alternately compress and rarefy air in column,
driving a wells turbine which turns with air travelling in either direction.
Floating:
Duck, clam, pelamis
Floating OWCs – backward bent duct buoy
Floating tapered channels
Tethered:
Wave power – (RE p305) The average total power in 1 metre length of wave crest is given by:
2
P = 0.5 H T where
Where P is the power in kW per metre of crest
H is the significant wave height
T is the average time between up/down movements of the surface through the mean level
95 % of the energy from a wave is contained in the layer between the surface and a depth h, equal to a
quarter of the wavelength i.e
λ
h = --------
4
28
Martin Parkinson’s T206 Glossary
Wind, impact of – (RE p270)
Advantages:
 Pretty much emission-free
 Generates 80 times the energy required to produce it
 Does not require consumption of water
Disadvantages:
 Noise: mechanical noise of generator and aerodynamic noise of blades – at 150 m roughly same
as within a quiet home, negligible over 400 m
 Electromagnetic interference
 Miliary aviation
 Visual impact
 Bird strikes – not major
Wind, offshore – (RE 286) Offshore wind is more expensive than onshore because:
Civil engineering for substructure
Higher electrical connection costs
Higher-spec materials needed in order to resist harsher environment (salt etc)
But –
offshore wind speeds generally higher
more feasible to use very large scale turbines (more energy per platform)
‘costs are expected to be competitive in the medium term’
(also might be increase in fishing yields (acting as reefs).
P287 – ‘within UK waters the potential annual electricity production from offshore wind is over 980 TWh
per year (almost 3 times the current annual UK electricity consumption).
Wind, onshore – (RE p267)
A rough estimate of the productivity of a windfarm can be obtained from:
3
Annual electricity production = K Vm At T
Where: K = 3.2
Vm is the site annual mean wind speed in metres per second
At is the swept are of a turbine in square metres
T is the number of turbines
Wind, potential – (ESS p285) estimate by EWEA et al 20% of world’s electricity could be produced by
2040. In the UK: ‘offshore and onshore wind are considered to have the greatest potential and lowest
costs of all the renewables’. Estimated (Border wind) that 40% of UK electricity could be generated from
0.03% of UK controlled sea bed – or 10% from 0.007%.
DTI 2006 figures show wind accounts for very slightly more electricity than hydro – 8.2% of renewable
sources (over 80% is biofuels and waste). But all renewables only accounted for 2% of primary energy
Wind, power – (RE) the power in the wind is given by:
3
P = 0.5 ρ A V
Where P is the power in watts
29
Martin Parkinson’s T206 Glossary
ρ is the density of air
A is the area under consideration
V is the velocity
(this formula is easily derivable from the standard equation for kinetic energy)
Wind speed-power curve – (RE p265) A graphic representation of the relationship between wind speed
and power output of a specific wind turbine. The curve has the following features:
Cut in speed – below this wind speed no power is generated. After it power rises steeply to the -
Rated power – after this point increases in wind speed will not increase the power output, until
the -
Shut down wind speed – when the turbine ceases to generate any power
Window energy balance - (eurosol instructions) – the daily energy balance during any particular month
is given by: window energy balance (kWh/m 2 /day) =
(transmission × incident solar) – (internal ref temp – monthly external temp) × U-value × 24 / 1000
In other words, the solar radiation entering a square metre of window is equal to the transmission
multiplied by the incident solar radiation on the outside. The average radiation entering per day in a
particular month will be equal to the average transmission multiplied by the average daily incident
radiation for that month.
The average rate of heat loss back out, in watts, will be equal to the temperature difference between the
inside (the Internal reference temperature) and the monthly average external air temperature, multiplied
by the window U-value. The daily loss in kWh is this rate multiplied by 24 and divided by 1000.
Yellowcake – see Nuclear fuel cycle
30